A semiconductor circuit or logic device may be designed for any of a wide variety of applications. Typically, the device includes logic circuitry to receive, manipulate or store input data, and the same or modified data is subsequently generated at an output terminal of the device. Depending on the type of logic device or the circuit environment in which the device is used, the device may include a regulator that provides an internal power signal that is independent of fluctuations of an external power signal.
A dynamic random access memory (DRAM), formed as an integrated circuit, is an example of such a semiconductor circuit or logic device having a regulator. Conventionally, the DRAM receives an external power signal (V.sub.CCX) having a voltage intended to maintain a voltage level (or range), for example, of 5 volts measured relative to common or ground. Internal to the DRAM, the regulator maintains an internal power signal (V.sub.CCR) at a designated level, for example, of 3.3 volts. Ideally, V.sub.CCR linearly tracks V.sub.CCX from zero volts to the designated level at which point V.sub.CCR remains constant as V.sub.CCX continues to increase in voltage or fluctuate above this level.
A number of previously implemented semiconductor power regulation circuits use a feedback-controlled p-channel transistor at the output of a control circuit, wherein the p-channel transistor is modulated once V.sub.CCX reaches the internal operating voltage level, at which point V.sub.CCR remains constant as described above. This approach is disadvantageous, however, because the feedback-controlled p-channel transistor acts in a manner similar to an operational amplifier whereby a substantial amount of current may be consumed during normal operation.
One known approach for mitigating this problem is to implement the control circuit at the input of the p-channel transistor with a low-power standby mode. In this mode, the larger p-channel transistor is deactivated when the integrated circuit is not in use so as to limit the excessive drain of drive current by the feedback-controlled p-channel transistor. Despite this limitation on current consumption, it is still desirable to reduce the overall level of current consumption. This is especially true for integrated circuit applications in which the integrated circuit is seldom not in use, in which case the beneficial contribution of the standby mode is nominal at best. Moreover, the standby approach introduces a delay to the operation of the integrated circuit, for example, during the transition from standby to normal operation. For fast-responding integrated circuits, such an additional delay is undesirable and often unacceptable.
U.S. Pat. No. 5,552,740 (the Casper patent) issued to Stephen L. Casper on Sep. 3, 1996 and is assigned to Micron Technology, Inc. The Casper patent describes an alternative to the more conventional feedback-controlled p-channel transistor-based regulator. Specifically, Casper describes a power-efficient power regulation circuit for use in semiconductor circuits powered by a power signal. The power regulation circuit includes an n-channel transistor which provides a regulated power signal having a stabilized voltage level for use by the semiconductor circuit. A bias pull-up circuit is coupled to the gate of the n-channel transistor and arranged for biasing the n-channel transistor so that it normally conducts current. A resistive circuit, including a resistive element arranged in series with a resistor-arranged p-channel transistor, is coupled to a source of the n-channel transistor and, in response to the regulated power signal, provides a feedback-control signal. A voltage control circuit, coupled to the bias pull-up circuit and the resistive circuit, is activated to control the n-channel transistor in response to the feedback control signal so as to provide the regulated output voltage. Unfortunately, the n-channel transistor may fluctuate by up to 200 or 300 millivolts when the circuit it drives switches between standby and active modes.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a regulator circuit that provides improved regulation during transitions between active and standby operation of the circuit that is powered by the regulator circuit.